1. Field of the Invention
The present invention relates to an image processing apparatus and, more particularly, to an image processing method and apparatus and an electronic device for receiving color image data corresponding to an arbitrary color space from a host computer, a color scanner, or the like, processing the image data, and outputting the image data to a color image forming apparatus.
2. Related Background Art
An image processing apparatus for receiving color image data from a host computer or the like and outputting the image data to a color printer to form an image is known.
In general, image data held by a host computer have various color spaces. For example, there are image data and the like which can be reproduced as desired images when the data are read by a scanner having a specific color space or when the data are displayed on a monitor having a specific color space. That is, even identical image data values of images expressed by R, G, and B data input from host computers do not necessarily represent the same color when the host computers differ in type or when the sources of the image data are different even if the host computers are identical to each other. In other words, there are a plurality of color spaces expressed by R, G, and B data. Color printers form images by using specific CMYK toners. For this reason, one specific color printer can express only one specific output color space.
Therefore, in order to form image data having various input color spaces in accordance with colors intended by a user, conversion from input color spaces to output color spaces must be performed in accordance with the characteristics of input images.
In a conventional method, parameters for LUT and masking circuits for performing color conversion from R, G, and B data into C, M, Y, and K data are stored in a RAM in advance, thereby performing conversion.
The following problems, however, are posed in the above-described conventional method in which image processing parameters used for a printing operation are stored in a RAM to express the characteristics of an input image.
1) There are a plurality of types of parameters for image processing. Of these parameters, optimal parameters can be discriminated only by a trial-and-error method, and wasteful trial printing operations are required. In addition, it is difficult to define the relationship between a change in each parameter and an effect on an output image. It is, therefore, difficult to determine which parameters should be changed.
2) Since a conversion result is a color space unique to each printer, different optimal parameters are required for different types of printers. In other words, optimal parameters need to be found for each type of printer.
That is, in the conventional method, it is difficult to set optimal parameters for the above-mentioned color space conversion.
As described above, there are various types of image forming apparatuses for receiving color raster image data from a host computer and the like and printing images. In this case, raster image data is image data describing an image as a group of pixels. Each pixel is described by various color component data values, e.g., 8-bit R, G, and B (Red, Green, and Blue) data, a total of 24 bits, or by 8-bit C, M, Y, and K (Cyan, Magenta, Yellow, and blacK) data, a total of 32 bits.
When image data are to be formed and edited in a host computer, various colors are displayed on the display screen, and colors to be used are selected from the displayed colors, thus forming and editing images. In this case, since images are held in the form of color raster image data, image data values (e.g., R, G, and B color component values) corresponding to the respective colors are predetermined, and the images are edited by using image data values corresponding to selected colors. The obtained raster image data are then transferred to the image forming apparatus to form images.
As in the conventional method, however, when designated colors are converted into raster image data on the computer side, conversion is performed regardless of the color characteristics of the image forming apparatus, thus posing the following problems.
1) Since the operator forms images on the basis of displayed colors, the image data values change depending on the type of display unit. PA1 2) Displayed colors differ from printed colors because the color characteristics of a display unit are generally different from those of an image forming apparatus. PA1 3) Even with the same input image data, different types of image forming apparatuses produce different output images. PA1 4) As the color characteristics of an image forming apparatus change over time, an output image changes in color.
With regard to the problem in 1) above, it is solved by using a specific color chart group as colors which can be selected. A color chart is obtained by selecting a specific color group and assigning a number to each color. A color can be specified by a color chart number. Each color chart is available as a printed matter. Therefore, if an image is formed on the basis of the colors of color charts on a printed matter by using colors displayed on a display unit only as reference colors, constant image data values can be obtained regardless of the type of display unit. In general, however, an image data value has different meanings for each type of printer, and hence the drawbacks 2) to 4) are left unsolved.